The long-term objective is to eradicate or arrest the growth of large established solid tumors by adoptively transferred T cells and to prevent the outgrowth of disseminated cancer. Eradication depends on T cells (i) eliminating the majority of cancer cells by direct antigen-specific (perforin-dependent) killing and (ii) destroying non-malignant tumor stroma cross-presenting antigens released from the cancer. The latter is needed to eliminate cancer cell variants responsible for recurrences. Radiation or chemotherapy causes a transient increase in stromal loading with tumor antigen and therefore synergizes with the therapeutic effect of T cells. Tumor eradication is obviously preferable to tumor arrest. However, for many aggressively growing rapidly lethal cancers that may have down-regulated MHC expression, long-term arrest of growth with equilibrium between the host and cancer would be an acceptable goal. This has been achieved in an experimental setting where T cells can only target and destroy stroma loaded with antigen released from cancer cells into the tumor microenvironment, but there are many unanswered questions. Thus, Aim 1 is to determine the mechanisms and the robustness of equilibrium induced by T cells targeting stroma only. Aim 2 determines the levels of mutant-self or normal self antigens needed to be expressed by the cancer cells to sensitize stroma for destruction and whether T cells with high-affinity TCRs can destroy stroma expressing lower levels of cross- presented target antigen without penalty of autoimmune destruction. Aim 3 will determine whether the principle of equilibrium by stromal destruction can be extended to micrometastatic or metastatic cancers including human cancers, such as ovarian and breast cancer growing in mice. Can micro-disseminated cancer cells or metastases be arrested, and do arrested cancers cease to disseminate cancer cells into the periphery? Optical imaging of established large tumors through a skin-fold window will be used to observe the in vivo effects of adoptively transferred T cells observed in real-time sequence with spatial definition. Understanding the reasons for the powerful equilibrium that can be exerted by targeting only stroma could suggest new strategies for more effective adoptive T cells therapy. PUBLIC HEALTH RELEVANCE: The proposed research examines the novel concept of permanently arresting tumor growth by targeting cancers indirectly with T cells killing stromal cells that present peptides derived from cancer-specific proteins, which are released from the cancer cells, on their MHC. By targeting and killing the stromal cells, multiple factors released by stroma, which promote and are needed for tumor growth, are eliminated. Thus, continuous destruction of stromal cells cross-presenting specific peptide/MHC complexes derived from cancer-specific proteins can cause long-term arrest of cancers including aggressively growing cancers that have become highly resistant to direct killing by T cells or other therapies.